Gas turbines have long used regenerators to improve efficiency. In the broadest terms, regenerators are heat exchangers that preheat air exiting the compressor section using thermal energy from exhaust exiting the expander section of the gas turbine. These include rotary, direct-contact regenerators and recuperators that use a heat-transfer surface as a wall between the air and the combustion gases.
Supercharging of gas turbines has a long history. Foster-Pegg describes some early systems from the 1960's. (See Foster-Pegg R. W., “Supercharging of Gas Turbines by Forced Draft Fans with Evaporative Intercooling,” American Society of Mechanical Engineers, Jan. 7, 1965, pp. 1-12.) Recent advances include variable-pressure supercharging such as described in U.S. Pat. No. 6,308,512.
Conventional wisdom is that compressors and expanders used for gas turbines should be of kinetic design. Standard textbooks, such as Fundamental of Gas Turbines by William Blathie and The Design of High-Efficiency Turbomachinery and Gas Turbines by David Gordon Wilson, concentrate almost exclusively on axial-flow and radial-flow machines for compressors and expanders.
In addition, conventional wisdom is that the regenerator should be downstream of the expander and that the optimum efficiency occurs at a low pressure ratio (i.e. combustor pressure to atmospheric pressure). High pressure ratios are generally found to produce worse mechanical efficiency for regenerative systems, which generally use pressure ratios of about 4 or less.
Copending application (Hoffman and Kopko, 20030182944) describes a highly supercharged gas turbine system. The present invention is an improvement of this system with special emphasis on the application of high-pressure supercharging to regenerative gas turbines such as found in microturbines and other small systems.